The present invention relates to an alloy plating bath containing tin and copper, method for plating with an alloy containing tin and copper using said plating bath and an article provided with a plated coating by said method.
In recent years, the concern about the effect of lead on the human body and the environment and about the risk of whisker production by pure tin plating has been increasing the demand for the development of a lead-free solder plating bath.
A tin-silver alloy, a tin-bismuth alloy and the like have been studied as the lead-free solder. However, the plating bath of the tin-silver alloy easily decomposes, and the plated coating of the tin-bismuth alloy is prone to cracks. Therefore, these alloys are disadvantageous.
A tin-copper alloy forms a eutectic composition with a copper content of 1.3 mole %. Although the alloy has a relatively high soldering temperature because of its melting point of 227xc2x0 C., it is unlikely to form cracks, excellent in soldering strength and less expensive than the tin-silver alloy or the like. For these reasons, the tin-copper alloy is a prospective lead-free solder.
Generally, electroplating with the alloy containing tin and copper is conducted while supplying tin(II) ions in the bath using a tin anode. However, since the copper salts contained in the bath have a standard electrode potential higher than the tin of the anode, chemical substitution occurs between the copper and tin. This may lead to the deposit of metallic copper on the anode. If the copper is deposited on the anode, the copper salt concentration in the bath is lowered and the bath composition changes. Therefore, the resulting plated coating of the tin-copper alloy tends to have inconstant composition. Particularly in the plating bath of the tin-copper alloy, the copper salt concentration in the bath is usually lower than the tin(II) salt concentration, and thus the change in the copper salt concentration greatly affect the composition of the coating.
Further, the composition of the plated coating of a tin-copper alloy, tin-copper-silver alloy, tin-copper-bismuth alloy and like alloys containing tin and copper tends to be dependent on cathodic current density. These alloys have the problem that when plating is carried out at a various current density ranging from high density to low density, the composition of the plated coating varies.
For example, in the tin-copper alloy plating, a tin-copper eutectic alloy having a low melting point can be obtained under the condition of a Cu content of 1.3 mole %. When the composition of the coating varies depending on the current density, it is not possible to constantly obtain the tin-copper alloy plated coating having the composition ratio which is suitable for the application.
Further, the plating bath containing tin and copper is likely to become turbid because of its unstability, unlike a tin plating bath, tin-lead alloy plating bath or the like. For example, the plating bath starts to become slightly turbid about one week after preparation, and the entire plating bath becomes turbid 1 month after the preparation.
The bath becomes turbid because divalent tin salt in the bath is oxidized to be tetravalent, thereby producing colloidal particles of tin oxide hydrate. Even the addition of an antioxidant can not completely prevent the bath from becoming turbid. Therefore, the Sn2+ content in the bath may be considerably lowered, which greatly inhibits obtaining a plated coating of an alloy containing tin and copper which has constant composition.
As the plating bath containing tin and copper, for example, Japanese Examined Patent Publication No. 1996-13185 discloses a tin alloy plating bath comprising (a) Sn2+ ion, (b) at least one metal ion selected from the group consisting of Ag+, Cu2+, In3+, Tl+ and Zn2+ and (c) a nonionic surfactant. Example 3 of this publication discloses a tin-copper alloy plating bath containing tin(II) methanesulfonate, copper methanesulfonate, methanesulfonic acid and ethylene oxide adduct of octyl phenol ethoxylate. Example 4 of the same publication discloses a tin-copper alloy plating bath containing tin(II) methanesulfonate, copper methanesulfonate, methanesulfonic acid and ethylene oxide adduct of laurylamine. According to this publication, the effects of these plating baths are that they can provide a low-melting-point plated coating similar to a tin-lead alloy coating without using lead; they impart good appearance and solderability to the plated coating; they facilitate the bath control; etc.
Meanwhile, Japanese Unexamined Patent Publication No. 1997-143786 discloses a silver alloy plating bath comprising (a) Ag+ ion; (b) at least one metal ion selected from the group consisting of Sn2+, Cu2+, In3+, Tl+, Zn2+ and Bi3+; (c) thiourea, acetyl thiourea, allylthiourea, trimethylthiourea and like thiourea compounds, thiazole compounds, dithiocarbamate compounds, thioglycol, thioglycolic acid, thiodiglycolic acid, xcex2-thiodiglycol and like sulfur-containing compounds; and (d) a nonion surfactant. Example 5 of the same publication describes a silver-tin-copper alloy plating bath comprising silver methanesulfonate, tin(II) methanesulfonate, copper methanesulfonate, methanesulfonic acid, xcex2-thiodiglycol, sodium N,Nxe2x80x2-diethyldithiocarbamate and ethylene oxide adduct of lauryl ether. According to this publication, the effects of the plating bath are that a fine plated coating and high throwing power can be obtained; the bath control is facilitated; etc.
However, the above plating baths disclosed in Nos. 1997-143786 and 1997-143786 have not completely solved the aforementioned problems such as deposition of copper on the anode by substitution, turbidness of the bath, dependence of the coating composition on the current density, etc.
An primary object of the present invention is to provide a plating bath containing tin and copper, the bath being capable of preventing deposition of copper on a tin anode by substitution, and having low dependence of plated coating composition on current density, high bath stability and resistance to turbidness.
In view of the aforesaid problems of the plating bath containing tin and copper, the inventors of the present invention conducted extensive research and found out that the above object can be achieved by adding a specific sulfur-containing compound to an alloy plating bath containing tin and copper. The present invention was accomplished based on this finding.
The present invention provides the alloy plating bath containing tin and copper and an article provided with a plated coating using the plating bath mentioned in the following.
1. A tin-copper alloy plating bath comprising:
(A) a soluble tin(II) compound;
(B) a soluble copper compound; and
(C) at least one sulfur-containing compound selected from the group consisting of the following compounds (i)-(v):
(i) a thiourea compound
(ii) a mercaptan compound
(iii) an aliphatic sulfide compound represented by the following formula (1):
Rexe2x80x94Raxe2x80x94[(Xxe2x80x94Rb)Lxe2x80x94(Yxe2x80x94Rc)Mxe2x80x94(Zxe2x80x94Rd)N]xe2x80x94Rfxe2x80x83xe2x80x83(1)
xe2x80x83(wherein the symbols represent the following:
M is an integer of 1-100, L and N are each 0 or an integer of 1-100; Y represents S or Sxe2x80x94S, X and Z are the same or different and each represents O, S or Sxe2x80x94S;
Ra represents C1-C12 straight-chain or branched-chain alkylene or 2-hydroxypropylene;
Rb, Rc and Rd are the same or different and each represents methylene, ethylene, propylene, 2-hydroxypropylene, butylene, pentylene or hexylene;
in Xxe2x80x94Rb, Yxe2x80x94Rc and Zxe2x80x94Rd, the position of each other is not limited and may be randomly positioned. When the bond Xxe2x80x94Rb""s, Yxe2x80x94Rc""s or Zxe2x80x94Rd""s are repeated, the Xxe2x80x94Rb""s, Yxe2x80x94Rc""s or Zxe2x80x94Rd""s may be composed of two or more kinds of bonds;
Re and Rf may be the same or different and each represents hydrogen, carboxyl, hydroxyl, alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, allyl, polycyclic cycloalkyl, aryl, polycyclic aryl, xe2x80x94O-alkyl, xe2x80x94S-alkyl, xe2x80x94O-alkenyl, xe2x80x94O-alkynyl, xe2x80x94O-aralkyl, xe2x80x94O-allyl, xe2x80x94O-polycyclic cycloalkyl, xe2x80x94O-acetyl, xe2x80x94O-aryl or xe2x80x94O-polycyclic aryl;
among Re and Rf, the groups other than hydrogen, carboxyl and hydroxyl may be substituted by at least one group selected from the group consisting of halogen, cyano, formyl, alkoxy, carboxyl, acyl, nitro and hydroxyl.),
(vi) a sulfide compound (excluding dithiodianiline) having a basic nitrogen atom represented by the following formula (2):
Rgxe2x80x94[(S)xxe2x80x94Rh]p-[(S)Yxe2x80x94Ri)]qxe2x80x83xe2x80x83(2)
xe2x80x83(wherein the symbols represent the following:
X and Y are each an integer of 1-4, p is 0 or an integer of 1-100, q is an integer of 1-100; in which
xe2x80x83(a) when p=0, Rg and Ri means (1) or (2) below:
(1) Rg and Ri are the same or different and each represents alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group, at least one of Rg and Ri having one or more basic nitrogen atom, or
(2) Rg and Ri are bonded to each other and form a monocyclic or polycyclic ring having one or more basic nitrogen atom;
in the above (1) and (2), Rg and Ri may be the same or different;
xe2x80x83(b) when p is an integer of 1-100, Rg, Rh and Ri mean (1) or (2) below:
(1) Rg and Ri represents alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group, Rh represents alkylene, alkenylene, alkynylene, aralkylene, cycloalkylene, polycyclic cycloalkylene, arylene, polycyclic arylene, heterocyclic group or polycyclic heterocyclic group, at least one of Rg, Rh and Ri having one or more basic nitrogen atom, or
(2) Rg and Rh, Rg and Ri, or Rh and Ri are bonded, or Rg and Rh, and Rh and Ri are simultaneously bonded, forming a monocyclic or polycyclic ring having one or more basic nitrogen atom;
in the above (1) and (2), Rg, Rh and Ri may be the same or different;
in the above (a) and (b), Rg, Rh and Ri may be substituted by at least one group selected from the group consisting of halogen, amino, cyano, formyl, alkoxy, carboxyl, acyl, nitro and hydroxy.), and
(v) a thiocrown ether compound.
2. The plating bath according to item 1, wherein the mercaptan compound comprises at least one basic nitrogen atom.
3. The plating bath according to item 1, wherein the thiocrown ether compound is at least one compound selected from the group consisting of the following (a)-(c):
(a) a thiocrown ether compound having at least one basic nitrogen atom,
(b) a thiocrown ether compound having at least one basic nitrogen atom and at least one oxygen atom,
(c) a compound in which at least two compounds selected from the group consisting of said thiocrown ether compounds (a) and said thiocrown ether compounds (b) are linked by a C1-C5 alkylene chain.
4. The plating bath according to item 1 which further comprising at least one compound selected from the group consisting of a compound having two or more nitrogen-containing aromatic rings in a molecule, unsaturated aliphatic carboxylic compound and a surfactant.
5. The plating bath according to item 4, wherein the surfactant is an alkylene oxide adduct of C8-C30 aliphatic amine.
6. A tin-copper-bismuth alloy plating bath comprising:
(A) a soluble tin(II) compound,
(B) a soluble copper compound,
(C) a soluble bismuth compound, and
(D) at least one sulfur-containing compound selected from the group consisting of the following compounds (i)-(v):
(i) a thiourea compound,
(ii) a mercaptan compound,
(iii) an aliphatic sulfide compound represented the following formula (1):
Rexe2x80x94Raxe2x80x94[(Xxe2x80x94Rb)Lxe2x80x94(Yxe2x80x94Rc)Mxe2x80x94(Zxe2x80x94Rd)N]xe2x80x94Rfxe2x80x83xe2x80x83(1)
xe2x80x83(wherein the symbols represent the following:
M is an integer of 1-100, L and N are each 0 or an integer of 1-100;
Y represents S or Sxe2x80x94S, X and Z are the same or different and each represents O, S or Sxe2x80x94S;
Ra represents a C1-C12 straight-chain or branched-chain alkylene, or 2-hydroxypropylene;
Rb, Rc and Rd are the same or different and each represents methylene, ethylene, propylene, 2-hydroxypropylene, butylene, pentylene or hexylene;
the positions of Xxe2x80x94Rb, Yxe2x80x94Rc and Zxe2x80x94Rd are not limited and may be randomly positioned. When the bond Xxe2x80x94Rb""s, Yxe2x80x94Rc""s or Zxe2x80x94Rd""s are repeated, the Xxe2x80x94Rb""s, Yxe2x80x94Rc""s or Zxe2x80x94Rd""s may be composed of two or more kinds of bonds;
Re and Rf are the same or different and each represents hydrogen, carboxyl, hydroxy, alkyl, alkenyl alkynyl, aralkyl, cycloalkyl, allyl, polycyclic cycloalkyl, aryl, polycyclic aryl, xe2x80x94O-alkyl, xe2x80x94S-alkyl, xe2x80x94O-alkenyl, xe2x80x94O-alkynyl, xe2x80x94O-aralkyl, xe2x80x94O-allyl, xe2x80x94O-polycyclic cycloalkyl, xe2x80x94O-acetyl, xe2x80x94O-aryl or xe2x80x94O-polycyclic aryl;
among Re and Rf, the groups other than hydrogen, carboxyl and hydroxy may be substituted by at least one group selected from the group consisting of halogen, cyano, formyl, alkoxy, carboxyl, acyl, nitro and hydroxy.),
(vi) a sulfide compound containing a basic nitrogen atom represented by the following formula (2):
Rgxe2x80x94[(S)Xxe2x80x94Rh]p-[(S)Yxe2x80x94Ri)]qxe2x80x83xe2x80x83(2)
xe2x80x83(wherein the symbols represent the following:
X and Y are each an integer of 1-4, p is 0 or an integer of 1-100, q is an integer of 1-100; in which
xe2x80x83(a) when p=0, Rg and Ri means (1) or (2) below:
(1) Rg and Ri are the same or different and each represents alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group, at least one of Rg and Ri having one or more basic nitrogen atom, or
(2) Rg and Ri are bonded to each other and form a monocyclic or polycyclic ring having one or more basic nitrogen atom;
in the above (1) and (2), Rg and Ri may be the same or different;
xe2x80x83(b) when p is an integer of 1-100, Rg, Rh and Ri mean (1) or (2) below:
(1) Rg and Ri represents alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group, Rh represents alkylene, alkenylene, alkynylene, aralkylene, cycloalkylene, polycyclic cycloalkylene, arylene, polycyclic arylene, heterocyclic group or polycyclic heterocyclic group, at least one of Rg, Rh and Ri having one or more basic nitrogen atom, or,
(2) Rg and Rh, Rg and Ri, or Rh and Ri are bonded, or Rg and Rh, and Rh and Ri are simultaneously bonded, forming a monocyclic or polycyclic ring having one or more basic nitrogen atom;
in the above (1) and (2), Rg, Rh and Ri may be the same or different;
in the above (a) and (b), Rg, Rh and Ri may be substituted by at least one group selected from the group consisting of halogen, amino, cyano, formyl, alkoxy, carboxyl, acyl, nitro and hydroxy.) and
(v) a thiocrown ether compound.
7. The plating bath according to item 6 wherein the mercaptan compound contains at least one basic nitrogen atom.
8. The plating bath according to item 6, wherein the thiocrown ether compound is at least one compound selected from the group consisting of the following compounds (a)-(c):
(a) a thiocrown ether compound having at least one basic nitrogen atom,
(b) a thiocrown ether compound having at least one basic nitrogen atom and at least one oxygen atom,
(c) a compound in which at least two compounds selected from the group consisting of said thiocrown ether compounds (a) and said thiocrown ether compounds (b) are linked by a C1-C5 alkylene chain.
9. The plating bath according to item 6 which further comprises at least one compound selected from the group consisting of a compound having two or more nitrogen-containing aromatic rings in a molecule, an unsaturated aliphatic carboxylic compound and a surfactant.
10. The plating bath according to item 9, wherein the surfactant is an alkylene oxide adduct of C8-C30 aliphatic amine.
11. A tin-copper-silver alloy plating bath compressing:
(A) a soluble tin(II) compound,
(B) a soluble copper compound,
(C) a soluble silver compound, and
(D) at least one sulfur-containing compound selected from the group consisting of the following compounds (i)-(iv):
(i) an aliphatic sulfide compound (excluding thiodiglycolic acid and thiodiglycol) represented by the following formula (1):
Rexe2x80x94Raxe2x80x94[(Xxe2x80x94Rb)Lxe2x80x94(Yxe2x80x94Rc)Mxe2x80x94(Zxe2x80x94Rd)N]xe2x80x94Rfxe2x80x83xe2x80x83(1)
xe2x80x83(wherein the symbols represent the following:
M is an integer of 1-100, L and N are each 0 or an integer of 1-100;
Y represents S or Sxe2x80x94S, X and Z are the same or different and each represents O, S or Sxe2x80x94S;
Ra represents a C1-C12 straight-chain or branched-chain alkylene, or 2-hydroxypropylene;
Rb, Rc and Rd are the same or different and each represents methylene, ethylene, propylene, 2-hydroxypropylene, butylene, pentylene or hexylene;
the positions of Xxe2x80x94Rb, Yxe2x80x94Rc and Zxe2x80x94Rd are not limited and may be randomly positioned. When the bond Xxe2x80x94Rb""s, Yxe2x80x94Rc""s or Zxe2x80x94Rd""s are repeated, the Xxe2x80x94Rb""s, Yxe2x80x94Rc""s or Zxe2x80x94Rd""s may be composed of two or more kinds of bonds;
Re and Rf are the same or different and each represents hydrogen, carboxyl, hydroxy, alkyl, alkenyl alkynyl, aralkyl, cycloalkyl, allyl, polycyclic cycloalkyl, aryl, polycyclic aryl, xe2x80x94O-alkyl, xe2x80x94S-alkyl, xe2x80x94O-alkenyl, xe2x80x94O-alkynyl, xe2x80x94O-aralkyl, xe2x80x94O-allyl, xe2x80x94O-polycyclic cycloalkyl, xe2x80x94O-acetyl, xe2x80x94O-aryl or xe2x80x94O-polycyclic aryl;
among Re and Rf, the groups other than hydrogen, carboxyl and hydroxy may be substituted by at least one group selected from the group consisting of halogen, cyano, formyl, alkoxy, carboxyl, acyl, nitro and hydroxy.),
(ii) a sulfide compound containing a basic nitrogen atom represented by the following formula (2):
Rgxe2x80x94[(S)Xxe2x80x94Rh]p-[(S)Yxe2x80x94Ri)]qxe2x80x83xe2x80x83(2)
xe2x80x83(wherein the symbols represent the following:
X and Y are each an integer of 1-4, p is 0 or an integer of 1-100, q is an integer of 1-100; in which
xe2x80x83(a) when p=0, Rg and Ri means (1) or (2) below:
(1) Rg and Ri are the same or different and each represents alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group, at least one of Rg and Ri having one or more basic nitrogen atom, or
(2) Rg and Ri are bonded to each other and form a monocyclic or polycyclic ring having one or more basic nitrogen atom;
in the above (1) and (2), Rg and Ri may be the same or different;
xe2x80x83(b) when p is an integer of 1-100, Rg, Rh and Ri mean (1) or (2) below:
(1) Rg and Ri represents alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group, Rh represents alkylene, alkenylene, alkynylene, aralkylene, cycloalkylene, polycyclic cycloalkylene, arylene, polycyclic arylene, heterocyclic group or polycyclic heterocyclic group, at least one of Rg, Rh and Ri having one or more basic nitrogen atom, or,
(2) Rg and Rh, Rg and Ri, or Rh and Ri are bonded, or Rg and Rh, and Rh and Ri are simultaneously bonded, forming a monocyclic or polycyclic ring having one or more basic nitrogen atom;
in the above (1) and (2), Rg, Rh and Ri may be the same or different;
in the above (a) and (b), Rg, Rh and Ri may be substituted by at least one group selected from the group consisting of halogen, amino, cyano, formyl, alkoxy, carboxyl, acyl, nitro and hydroxy.),
(iii) a mercaptan compound having at least one basic nitrogen atom, and
(iv) a thiocrown ether compound.
12. The plating bath according to item 11, wherein the thiocrown ether compound is at least one compound selected from the group consisting of the following (a)-(c):
(a) a thiocrown ether compound having at least one basic nitrogen atom,
(b) a thiocrown ether compound having at least one basic nitrogen atom and at least one oxygen atom,
(c) a compound in which at least two compounds selected from the group consisting of said thiocrown ether compounds (a) and said thiocrown ether compounds (b) are linked by a C1-C5 alkylene chain.
13. The plating bath according to item 11 which further comprises at least one compound selected from the group consisting of a compound having two or more nitrogen-containing aromatic rings in a molecule, an unsaturated aliphatic carboxylic compound and a surfactant.
14. The plating bath according to item 13, wherein the surfactant is an alkylene oxide adduct of C8-C30 aliphatic amine.
15. A plating method for depositing a tin-copper alloy, the method comprising immersing an article to be plated in the plating bath of item 1 and forming a tin-copper alloy plated coating by electroplating.
16. A plating method for depositing a tin-copper-bismuth alloy, the method comprising immersing an article to be plated in the plating bath of item 6 and forming a tin-copper-bismuth alloy plated coating by electroplating.
17. A plating method for depositing a tin-copper-silver alloy, the method comprising immersing an article to be plated in the plating bath of item 11 and forming a tin-copper-silver alloy plated coating by electroplating.
18. An article which is provided with a tin-copper alloy plated coating by the plating method of item 15.
19. An article which is provided with a tin-copper-bismuth alloy plated coating by the plating method of item 16.
20. An article which is provided with a tin-copper-silver alloy plated coating by the plating method of item 17.
The present invention relates to an alloy plating bath containing tin and copper, more specifically to a tin-copper alloy plating bath, a tin-copper-silver alloy plating bath and a tin-copper-bismuth alloy plating bath.
Soluble Metal Compound
In these plating baths, any organic or inorganic soluble metal compound which can produce corresponding metal ions in water can be used as a metal compound.
Examples of the soluble tin(II) compound include tin(II) salts of organic sulfonic acid such as methanesulfonic acid, ethanesulfonic acid, 2-propanolsulfonic acid, p-phenolsulfonic acid and like, tin(II) borofluoride, tin(II) sulfosuccinate, tin(II) sulfate, tin(II) oxide, tin(II) chloride and the like. These soluble tin(II) compounds may be used singly or in combination of two or more kinds.
Examples of the soluble copper compound include copper salts of the aforementioned organic sulfonic acids, copper sulfate, copper chloride, copper oxide, copper carbonate, copper acetate, copper pyrophosphate, copper oxalate and the like. These soluble copper compounds may be used singly or in combination of two or more kinds.
Examples of the soluble silver compound include silver sulfate, silver sulfite, silver carbonate, silver nitrate, silver oxide, silver sulfosuccinate, silver salts of the above-mentioned organic sulfonic acids, silver citrate, silver tartrate, silver gluconate, silver oxalate and the like. These soluble silver compounds may be used singly or in combination of two or more kinds.
Example of the soluble bismuth compound include bismuth oxide, bismuth chloride, bismuth bromide, bismuth nitrate, bismuth sulfate, bismuth salts of the above organic sulfonic acids, bismuth sulfosuccinate and the like. These soluble bismuth compounds may be used singly or in combination of two or more kinds.
Among the above-mentioned soluble metal compounds, the amount of the soluble tin(II) compound is preferably about 0.01-2 mole/l, more preferably about 0.05-1 mole/l.
The amount of the soluble copper compound is preferably about 0.0001-0.5 mole/l, more preferably about 0.0005-0.05 mole/l.
The amount of the soluble bismuth compound is preferably about 0.00003-0.05 mole/l, more preferably about 0.0002-0.02 mole/l.
The amount of the soluble silver compound is preferably about 0.00008-0.1 mole/l, more preferably about 0.0004-0.03 mole/l.
The ratio of the metal compounds in the tin-copper alloy plating bath, tin-copper-silver alloy plating bath and tin-copper-bismuth alloy plating bath can be suitably selected depending on the desired composition of the plated alloy coating. For example, in order to obtain a deposit of a tin-rich plated alloy coating containing tin and copper, which can be a substitute for a solder coating in which the weight ratio of tin to lead is 9:1, the molar ratio of the tin compound and other metal compounds in the plating bath may be about 99:1 to about 85:15.
In the tin-copper alloy plating bath, tin-copper-silver alloy plating bath and tin-copper-bismuth alloy plating bath, the total amount of the soluble metal compounds is preferably about 0.0101-2.65 mole/l, more preferably about 0.0505-1.1 mole/l.
Acids and Salts Thereof
The plating bath containing tin and copper of the present invention comprises, as a basic component, at least one component selected from the group consisting of acids and their salts. Useful acids include organic sulfonic acid, aliphatic carboxylic acid and like organic acids; sulfuric acid, hydrochloric acid, fluoroboric acid, fluorosilicic acid, sulfamic acid and like inorganic acids. In the present invention, particularly among the above acid and their salts, the organic sulfonic acids, their salts and the like are preferable in terms of the metal salts dissolvability, wastewater disposability, etc.
Useful organic sulfonic acids include alkanesulfonic acid, alkanolsulfonic acid, aromatic sulfonic acid and the like.
Among the above acids, as the alkanesulfonic acids may be used a compound represented by the chemical formula CnH2n+1SO3H (for example, n=1 to 11). Examples of the alkanesulfonic acid include methanesulfonic acid, ethanesulfonic acid, 1-propanesulfonic acid, 2-propanesulfonic acid, 1-buthanesulfonic acid, 2-buthanesulfonic acid, pentanesulfonic acid, hexanesulfonic acid, decanesulfonic acid, dodecanesulfonic acid and the like.
As the alkanolsulfonic acid may be used a compound represented by the chemical formula:
CmH2m+1xe2x80x94CH(OH)xe2x80x94CpH2pxe2x80x94SO3H
(for example, m=0 to 6, p=1 to 5). Examples of the alkanolsulfonic acid include 2-hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid (2-propanolsulfonic acid), 2-hydroxybutane-1-sulfonic acid, 2-hydroxypentane-1-sulfonic acid, 1-hydroxypropane-2-sulfonic acid, 3-hydroxypropane-1-sulfonic acid, 4-hydroxybutane-1-sulfonic acid, 2-hydroxyhexane-1-sulfonic acid, 2-hydroxydecane-1-sulfonic acid, 2-hydroxydodecane-1-sulfonic acid and the like.
Examples of the aromatic sulfonic acid include benzenesulfonic acid, alkylbenzenesulfonic acid, phenolsulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, naphtholsulfonic acid and the like. More specifically, useful are 1-naphthalenesulfonic acid, 2-naphthalenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, p-phenolsulfonic acid, cresolsulfonic acid, sulfosalicylic acid, nitrobenzenesulfonic acid, sulfobenzoic acid, diphenylamine-4-sulfonic acid and the like.
The salts of the above acids may be any soluble salts of these acids, for example, Na salts, K salts and like alkali metal salts, Ca salts and like alkali earth metal salts, diethylamine salts and like alkyl amine salts, ammonium salts and the like.
Among the above organic sulfonic acids and their salts, preferable are methanesulfonic acid, ethanesulfonic acid, 2-propanolsulfonic acid, phenolsulfonic acid, the salts of these acids and the like.
In the alloy plating bath containing tin and copper of the present invention, the above acids and their salts may be used singly or in combination of two or more kinds. The amount of the acids and their salts is preferably about 0.01-50 mole/l, more preferably about 0.1-10 mole/l.
Sulfur-containing Compound
The alloy plating bath containing tin and copper of the present invention essentially contains a specific sulfur-containing compound as an additive.
The sulfur-containing compound used as an additive varies depending on the kind of the alloy plating bath. In the following, the sulfur-containing compounds are described by the types of the alloy plating baths for which the sulfur-containing compound is useful.
Sulfur-containing Compound in Tin-copper Alloy Plating Bath
In the tin-copper alloy plating bath, as the sulfur-containing compound is used at least one compound selected from the group consisting of (i)-(v) listed below. It should be noted that the sulfide compound containing a basic nitrogen atom represented by the formula (2) does not include dithiodianiline.
(i) a thiourea compound,
(ii) a mercaptan compound,
(iii) an aliphatic sulfide compound represented by the following formula (1):
Rexe2x80x94Raxe2x80x94[(Xxe2x80x94Rb)Lxe2x80x94(Yxe2x80x94Rc)Mxe2x80x94(Zxe2x80x94Rd)N]xe2x80x94Rfxe2x80x83xe2x80x83(1)
xe2x80x83(wherein the symbols represent the following:
M is an integer of 1-100, L and N are each 0 or an integer of 1-100;
Y represents S or Sxe2x80x94S, X and Z are the same or different and each represents O, S or Sxe2x80x94S;
Ra represents a C1-C12 straight-chain or branched-chain alkylene, or 2-hydroxypropylene;
Rb, Rc and Rd are the same or different and each represents methylene, ethylene, propylene, 2-hydroxypropylene, butylene, pentylene or hexylene;
the positions of Xxe2x80x94Rb, Yxe2x80x94Rc and Zxe2x80x94Rd are not restricted and may be random. When the bond Xxe2x80x94Rb""s, Yxe2x80x94Rc""s or Zxe2x80x94Rd""s are repeated, the Xxe2x80x94Rb""s, Yxe2x80x94Rc""s or Zxe2x80x94Rd""s may be composed of two or more kinds of bonds;
Re and Rf are the same or different and each represents hydrogen, carboxyl, hydroxy, alkyl, alkenyl alkynyl, aralkyl, cycloalkyl, allyl, polycyclic cycloalkyl, aryl, polycyclic aryl, xe2x80x94O-alkyl, xe2x80x94S-alkyl, xe2x80x94O-alkenyl, xe2x80x94O-alkynyl, xe2x80x94O-aralkyl, xe2x80x94O-allyl, xe2x80x94O-polycyclic cycloalkyl, xe2x80x94O-acetyl, xe2x80x94O-aryl or xe2x80x94O-polycyclic aryl;
among Re and Rf, the groups other than hydrogen, carboxyl and hydroxy may be substituted by at least one group selected from the group consisting of halogen, cyano, formyl, alkoxy, carboxyl, acyl, nitro and hydroxy.),
(vi) a sulfide compound (excluding dithiodianiline) containing a basic nitrogen atom represented by the following formula (2):
Rgxe2x80x94[(S)xxe2x80x94Rh]p-[(S)yxe2x80x94Ri)]qxe2x80x83xe2x80x83(2)
xe2x80x83(wherein the symbols represent the following:
X and Y are each an integer of 1-4, p is 0 or an integer of 1-100, q is an integer of 1-100; in which
xe2x80x83(a) when p=0, Rg and Ri means (1) or (2) below:
(1) Rg and Ri are the same or different and each represents alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group, at least one of Rg and Ri having one or more basic nitrogen atom, or
(2) Rg and Ri are bonded to each other and form a monocyclic or polycyclic ring having one or more basic nitrogen atom;
In the above (1) and (2), Rg and Ri may be the same or different;
xe2x80x83(b) when p is an integer of 1-100, Rg, Rh and Ri mean (1) or (2) below:
(1) Rg and Ri represents alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group, Rh represents alkylene, alkenylene, alkynylene, aralkylene, cycloalkylene, polycyclic cycloalkylene, arylene, polycyclic arylene, heterocyclic group or polycyclic heterocyclic group, at least one of Rg, Rh and Ri having one or more basic nitrogen atom, or,
(2) Rg and Rh, Rg and Ri, or Rh and Ri are bonded, or Rg and Rh, and Rh and Ri are simultaneously bonded, forming a monocyclic or polycyclic ring having one or more basic nitrogen atom;
in the above (1) and (2), Rg, Rh and Ri may be the same or different;
in the above (a) and (b), Rg, Rh and Ri may be substituted by at least one group selected from the group consisting of halogen, amino, cyano, formyl, alkoxy, carboxyl, acyl, nitro and hydroxy.), and (v) a thiocrown ether compound.
The tin-copper alloy plating bath comprising the aforementioned specific sulfur-containing compound is effective in preventing the deposition of copper on the tin anode by substitution in electroplating. In addition, the tin-copper alloy plating bath can form a plated coating having low dependency of composition on the current density. The tin-copper alloy plating bath has high bath stability and prevents turbidness.
Among the sulfur-containing compounds useful for the tin-copper plating bath, as the thiourea compound may be used at least one compound selected from the group consisting of thiourea and its derivatives. Examples of the thiourea derivatives include 1,3-dimethylthiourea, trimethylthiourea, diethylthiourea, N,Nxe2x80x2-diisopropylthiourea, allylthiourea, acetylthiourea, ethylenethiourea, 1,3-diphenylthiourea, thiourea dioxide and the like.
As the mercaptan compound may be used any compound having a mercapto group in its molecule. Examples of such compound include thioglycol, thioglycolic acid, mercaptosuccinic acid, mercaptolactic acid, acetylcysteine, penicillamine and like aliphatic mercaptan compounds; 5-mercapto-1,3,4-triazole, 3-mercapto-4-methyl-4H-1,2,4-triazole and like aromatic or heterocyclic mercaptan compounds and the like.
Among these mercaptan compounds, preferable are penicillamine, 5-mercapto-1,3,4-triazole, 3-mercapto-4-methyl-4H-1,2,4-triazole and like mercaptan compounds having at least one basic nitrogen atom.
In the formula (1) and formula (2) which represent the sulfide compounds useful for the tin-copper plating bath of the invention, a preferable alkyl group is C1-C6 straight-chain or branched-chain alkyl; a preferable alkenyl is C2-C6 straight-chain or branched chain alkenyl; a preferable alkynyl is C2-C6 straight-chain or branched-chain alkynyl; preferable aralkyl include benzyl, phenethyl, styryl and the like; preferable cycloalkyl include cyclopentyl, cyclohexyl and the like; preferable polycyclic cycloalkyl include adamantyl and the like; preferable aryl include phenyl, cumenyl and the like; preferable polycyclic aryl include naphthyl, phenanthryl and the like; preferable heterocyclic groups and polycyclic heterocyclic groups include groups derived from pyridine ring, pyrrole ring, pyrazine ring, pyridazine ring, thiazole ring, thiadiazole ring, imidazoline ring, imidazole ring, thiazoline ring, triazole ring, tetrazole ring, picoline ring, furazan ring, piperidine ring, piperazine ring, triazine ring, morpholine ring, benzothiazole ring, benzimidazole ring, quinoline ring, quinoxaline ring, pteridine ring, phenanthroline ring, phenazine ring, indoline ring, perhydroindoline ring and the like.
Preferable examples of the alkylene, alkenylene, alkynylene, aralkylene, cycloalkylene, polycyclic cycloalkylene, polycyclic arylene, heterocyclic group and polycyclic heterocyclic group represented by Rh in the formula (2) are the divalent groups derived from the groups mentioned as the examples of alkyl, alkenyl, alkynyl, aralkyl, cycloalkyl, polycyclic cycloalkyl, aryl, polycyclic aryl, heterocyclic group or polycyclic heterocyclic group.
Among Re and Rf in the above formula (1), the groups other than hydrogen, carboxyl and hydroxy may have at least one substituent selected from the group consisting of halogen (chlorine, fluorine, bromine, etc.), cyano, formyl, alkoxy (preferably C1-C6 alkoxy), carboxyl, acyl (preferably C1-C6 acyl), nitro and hydroxy. Rg, Rh and Ri in the formula (2) may be substituted by at least one group selected from the group consisting of the above-mentioned substituents and amino group.
The aliphatic sulfide compound represented by the formula (1) has a sulfide bond or disulfide bond in its molecule and it does not contain a basic nitrogen atom. Examples of such aliphatic sulfide compound are as follows. In the structural formulas, Ph represents a phenyl group.
(1) Thiobis(diethyleneglycol) represented by Hxe2x80x94(OCH2CH2)2xe2x80x94Sxe2x80x94(CH2CH2O)2xe2x80x94H
(2) Thiobis(hexaethylene glycol)
(3) Thiobis(pentadecaglycelol) represented by Hxe2x80x94(OCH2CH(OH)CH2)15xe2x80x94Sxe2x80x94(CH2CH(OH)CH2O)15xe2x80x94H
(4) Thiobis(icosaethyleneglycol) represented by Hxe2x80x94(OCH2CH2)20xe2x80x94Sxe2x80x94(CH2CH2O)20xe2x80x94H
(5) Thiobis(pentacontaethyleneglycol)
(6) 4,10-dioxa-7-thiatridecane-2,12-diol represented by HOxe2x80x94CH(CH3)CH2xe2x80x94OCH2CH2xe2x80x94SCH2CH2xe2x80x94OCH2CH(CH3)xe2x80x94OH
(7) Thiodiglycerin represented by HOCH2CH(OH)CH2xe2x80x94Sxe2x80x94CH2CH(OH)CH2OH
(8) Thiobis(triglycerin) represented by Hxe2x80x94(OCH2CH(OH)CH2)3xe2x80x94Sxe2x80x94(CH2CH(OH)CH2O)3xe2x80x94H
(9) 2,2xe2x80x2-thiodibutanolbis(octaethyleneglycolpentaglycerol)ether represented by Hxe2x80x94(OCH2CH(OH)CH2)5xe2x80x94(OCH2CH2)8xe2x80x94OC4H8xe2x80x94SC4H8xe2x80x94Oxe2x80x94(CH2CH2O)8xe2x80x94(CH2CH(OH)CH2O)5xe2x80x94H
(10) Thiobis(octaethyleneglycol)bis(2-chloroethyl)ether represented by Clxe2x80x94CH2CH2CH2xe2x80x94(OCH2CH2)8xe2x80x94Sxe2x80x94(CH2CH2O)8xe2x80x94CH2CH2CH2xe2x80x94Cl
(11) Thiobis(decaethyleneglycol)bis(carboxymethyl)ether
(12) Thiobis(dodecaethyleneglycol)bis(2-nitroethyl)ether
(13) Thiodiglycolbis(carboxymethyl)ether represented by HOOCCH2OCH2CH2xe2x80x94Sxe2x80x94CH2CH2OCH2COOH
(14) Dithiodiglycolbis(carboxymethyl)ether represented by HOOCCH2OCH2CH2xe2x80x94Sxe2x80x94Sxe2x80x94CH2CH2OCH2COOH
(15) Thiobis(dodecaethyleneglycol) represented by Hxe2x80x94(OCH2CH2)12xe2x80x94Sxe2x80x94(CH2CH2O)12xe2x80x94H
(16) Dithiobis(hentetracontaethyleneglycol) represented by Hxe2x80x94(OCH2CH2)41xe2x80x94Sxe2x80x94Sxe2x80x94(CH2CH2O)41xe2x80x94H
(17) Dithiobis(icosaethyleneglycolpentapropyleneglycol) represented by Hxe2x80x94(OC3H6)5xe2x80x94(OC2H4)20xe2x80x94Sxe2x80x94Sxe2x80x94(OC2H4)20xe2x80x94(OC3H6)5xe2x80x94H
(18) Dithiobis(triglycerol) represented by Hxe2x80x94(OCH2CH(OH)CH2)3xe2x80x94Sxe2x80x94Sxe2x80x94(CH2CH(OH)CH2O)3xe2x80x94H
(19) Dithiobis(decaglycelol)
(20) 3,6-Dithiaoctane-1,8-diol represented by HOCH2CH2Sxe2x80x94CH2CH2xe2x80x94SCH2CH2OH
(21) 1,3-Propanedithiolbis(decaethyleneglycol)thioether represented by Hxe2x80x94(OC2H4)10xe2x80x94Sxe2x80x94C3H6xe2x80x94Sxe2x80x94(OC2H4)10xe2x80x94H
(22) 1,4-Buthanedithiolbis(pentadecaglycerol)thioether represented by Hxe2x80x94(OCH2CH(OH)CH2)15xe2x80x94Sxe2x80x94C4H8xe2x80x94Sxe2x80x94(CH2CH(OH)CH2O)15xe2x80x94H
(23) 1,3-Dithioglycerolbis(pentaethyleneglycol)thioether represented by Hxe2x80x94(OCH2CH2)5xe2x80x94SCH2CH(OH)CH2Sxe2x80x94(CH2CH2O)5xe2x80x94H
(24) 1,2-Ethanedithiolbis(penta(1-ethyl)ethyleneglycol)thioether represented by Hxe2x80x94(OCH(C2H5)CH2)5xe2x80x94SC2H4Sxe2x80x94(CH2CH(C2H5)O)5xe2x80x94H
(25) 1,3-Dithioglycerolbis(di(1-ethyl)ethyleneglycol)thioether represented by Hxe2x80x94(OCH(CH3)CH2)2xe2x80x94SCH2CH(OH)CH2Sxe2x80x94(CH2CH(CH3)O)2xe2x80x94H
(26) 2-Mercaptoethylsulfide bis(hexatriacontaethylene-glycol) represented by H-(OC2H4)18xe2x80x94SC2H4xe2x80x94SC2H4xe2x80x94Sxe2x80x94(C2H4O)18xe2x80x94H
(27) 2-Mercaptoethylsulfidebis(icosaethyleneglycol)di-methylether represented by CH3xe2x80x94(OC2H4)10xe2x80x94SC2H4xe2x80x94SC2H4xe2x80x94Sxe2x80x94(C2H4O)10-CH3 
(28) 2-Mercaptoethyletherbis(diethyleneglycol) represented by Hxe2x80x94(OC2H4)2xe2x80x94Sxe2x80x94CH2CH2OCH2CH2xe2x80x94Sxe2x80x94(C2H4O)2xe2x80x94H
(29) Thiodiglyceroltetra(decaethyleneglycol)ether represented by the above formula (6)
(30) Diethyleneglycolmonomethylthioether represented by CH3xe2x80x94Sxe2x80x94(CH2CH2O)2xe2x80x94H
(31) Decaglycerolmono(6-methylthiohexyl)thioether represented by CH3xe2x80x94Sxe2x80x94C6H12xe2x80x94Sxe2x80x94(CH2CH(OH)CH2O)10xe2x80x94H
(32) 2-Mercaptoethylsulfide-xcfx89-{(2-bromoethyl)icosaethyleneglycol}thioether-xcfx89xe2x80x2-{(2-bromoethyl)hectaethyleneglycol}thioether represented by BrCH2CH2xe2x80x94(OCH2CH2)20xe2x80x94(Sxe2x80x94CH2CH2)3xe2x80x94(OCH2CH2)100xe2x80x94OCH2CH2Br
(33) 1,4-Butanediol-xcfx89-{(2-benzyloxy-1-methyl)ethyl}thioether-xcfx89xe2x80x2-(decapropyleneglycoloctacontaethyleneglycol)thioether represented by PhCH2OCH2CH(CH3)xe2x80x94Sxe2x80x94C4H8xe2x80x94Sxe2x80x94(CH2CH2O)80xe2x80x94(CH2CH(CH3)O)10xe2x80x94H
(34) Dithiobis(icosaethyleneglycol)bis(2-methyl-thioethyl)ether represented by CH3xe2x80x94Sxe2x80x94CH2CH2xe2x80x94(OCH2CH2)20xe2x80x94Sxe2x80x94Sxe2x80x94(CH2CH2O)20xe2x80x94CH2CH2Sxe2x80x94CH3 
(35) 1,2-Ethanediol-xcfx89-(4-methoxybenzyl)thioether-xcfx89xe2x80x2-(pentacontaethyleneglycol)thioether represented by CH3Oxe2x80x94Phxe2x80x94CH2Sxe2x80x94CH2CH2xe2x80x94(CH2CH2O)50xe2x80x94H
(36) Triacontaethyleneglycolmono(4-cyanobenzyl)thioether represented by NCxe2x80x94Phxe2x80x94CH2Sxe2x80x94(CH2CH2O)30xe2x80x94H
(37) Thiobis(pentadecaethyleneglycol)bisallylether represented by CH2xe2x95x90CHCH2xe2x80x94(OCH2CH2)15xe2x80x94Sxe2x80x94(CH2CH2O)15xe2x80x94CH2CHxe2x95x90CH2 
(38) Tricosaethyleneglycolmono(4-formylphenetyl)thioether represented by OHCxe2x80x94Phxe2x80x94CH2CH2xe2x80x94Sxe2x80x94(CH2CH2O)23xe2x80x94H
(39) Pentadecaethyleneglycolmono{(acetylmethyl)thioethyl}thioether represented by CH3COCH2xe2x80x94Sxe2x80x94CH2CH2xe2x80x94Sxe2x80x94(CH2CH2O)15xe2x80x94H
(40) 1,2-Ethanediol-xcfx89-(glycidyl)thioether-xcfx89xe2x80x2-icosaethyleneglycolthioether represented by the following formula 
(41) Octadecaethyleneglycolbis(2-methylthioethyl)ether represented by CH3xe2x80x94Sxe2x80x94CH2CH2COxe2x80x94(CH2CH2O)18xe2x80x94CH2CH2Sxe2x80x94CH3 
(42) Hexadecaethyleneglycolmono(2-methylthioethyl)thioether represented by CH3xe2x80x94Sxe2x80x94CH2CH2xe2x80x94Sxe2x80x94(CH2CH2O)16xe2x80x94H
(43) Icosaethyleneglycolmonomethylthioether represented by CH3xe2x80x94Sxe2x80x94(CH2CH2O)20xe2x80x94H
(44) Undecaethyleneglycoldi(n-propyl)thioether represented by C3H7xe2x80x94Sxe2x80x94(CH2CH2O)10xe2x80x94CH2CH2Sxe2x80x94C3H7 
(45) Dodecaethyleneglycolbis(2-hydroxyethyl)thioether represented by HOCH2CH2Sxe2x80x94(CH2CH2O)11xe2x80x94CH2CH2Sxe2x80x94CH2CH2OH
(46) Undecaethyleneglycoldimethylthioether
(47) Pentatriacontaethyleneglycolmono(2-n-butyldithioethyl)dithioether represented by C4H9xe2x80x94Sxe2x80x94Sxe2x80x94CH2CH2xe2x80x94Sxe2x80x94Sxe2x80x94(CH2CH2O)35xe2x80x94H
(48) 4,8,12-trithiapentadecane-1,2,6,10,14,15-hexaol represented by HOCH2CH(OH)CH2xe2x80x94Sxe2x80x94CH2CH(OH)CH2xe2x80x94Sxe2x80x94CH2CH(OH)CH2xe2x80x94Sxe2x80x94CH2CH(OH)CH2OH
(49) Icosaglycerolmono(2-ethylthioethyl)thioether represented by C2H5xe2x80x94Sxe2x80x94CH2CH2xe2x80x94Sxe2x80x94(CH2CH(OH)CH2O)20xe2x80x94H
(50) Triacontaethyleneglycolmono(2-methylthioethyl)thioether represented by CH3xe2x80x94Sxe2x80x94CH2CH2xe2x80x94Sxe2x80x94(C2H4O)30xe2x80x94H
(51) Dithiobis(icosaethyleneglycol)dibenzylether represented by Phxe2x80x94CH2xe2x80x94(OC2H4)20xe2x80x94Sxe2x80x94Sxe2x80x94(C2H4O)20xe2x80x94CH2xe2x80x94Ph
(52) Tridecaethyleneglycolmonomethylthioether represented by CH3xe2x80x94Sxe2x80x94(CH2CH2O)10xe2x80x94H
(53) Hexadecaethyleneglycol dimethylthioether represented by CH3xe2x80x94Sxe2x80x94(CH2CH2O)15xe2x80x94CH2CH2Sxe2x80x94CH3 
(54) 1,2-Ethanedithiolbis(icosaethyleneglycol)thioether represented by Hxe2x80x94(OCH2CH2)20xe2x80x94Sxe2x80x94CH2CH2xe2x80x94Sxe2x80x94(CH2CH2O)20xe2x80x94H
(55) Dithiobis(pentadecaethyleneglycol) represented by Hxe2x80x94(OCH2CH2)15xe2x80x94Sxe2x80x94Sxe2x80x94(CH2CH2O)15xe2x80x94H
(56) 3,3xe2x80x2-thiodipropanol represented by HOxe2x80x94CH2CH2CH2xe2x80x94Sxe2x80x94CH2CH2CH2xe2x80x94OH
The sulfide compound represented by the above formula (2) has one or more bonds in its molecule, the bond being at least one bond selected from the group consisting of sulfide, disulfide, trisulfide and tetrasulfide bonds. The sulfide compound also contains at least one basic nitrogen atom. Such sulfide compound include aliphatic sulfide compound, aromatic sulfide compound and like various sulfide compounds. However, the tin-copper alloy plating bath of the present invention does not include dithiodianiline.
Such sulfide compound containing a basic nitrogen atom represented by the formula (2) is described specifically. For example, in 2,2xe2x80x2-di(1-methylpyrrolyl)disulfide, both pyrrole rings at both ends of a disulfide bond have a basic nitrogen atom each, while in 2,2xe2x80x2-dithiodianiline, benzene rings at both ends of a disulfide bond each have a substituted amino group containing a basic nitrogen atom.
Examples of the sulfide compound having at least one basic nitrogen atom represented by the formula (2) include the followings.
(1) 2-Ethylthioaniline
(2) 2-(2-aminoethyldithio)pyridine
(3) 2,2xe2x80x2-dithiadiazolyldisulfide
(4) 5,5xe2x80x2-di(1,2,3-triazolyl)disulfide
(5) 2,2xe2x80x2-dipyradinyldisulfide
(6) 2,2xe2x80x2-dipyridyldisulfide
(7) 4,4xe2x80x2-dipyridyldisulfide
(8) 2,2xe2x80x2-diamino-4,4xe2x80x2-dimethyldiphenyldisulfide
(9) 2,2xe2x80x2-dipyridazinyldisulfide
(10) 5,5xe2x80x2-dilpyrimidinyldisulfide
(11) 2,2xe2x80x2-di(5-dimethylaminothiadiazolyl)disulfide
(12) 5,5xe2x80x2-di(1-methyltetrazolyl)disulfide
(13) 2,2xe2x80x2-di(1-methylpyrrolyl)disulfide
(14) 2-pyridyl-2-hydroxyphenyldisulfide
(15) 2,2xe2x80x2-dipiperidyldisulfide
(16) 2,2xe2x80x2-dipyridylsulfide
(17) 2,6-di(2-pyridyldithio)pyridine
(18) 2,2xe2x80x2-dipiperazinyldisulfide
(19) 2,2xe2x80x2-di(3,5-dihydroxypyrimidinyl)disulfide
(20) 2,2xe2x80x2-diquinolyldisulfide
(21) 2,2xe2x80x2-di{6-(2-pyridyl)}pyridyldisulfide
(22) 2,2xe2x80x2-xcex1-picolyldisulfide
(23) 2,2xe2x80x2-di(8-hydroxyquinolyl)disulfide
(24) 5,5xe2x80x2-diimidazolyldisulfide
(25) 2,2xe2x80x2-dithiazolyldisulfide
(26) 2-pyridyl-2-aminophenyldisulfide
(27) 2-pyridyl-2-quinolyldisulfide
(28) 2,2xe2x80x2-dithiazolinyldisulfide
(29) 2,2xe2x80x2-di(4,5-diamino-6-hydroxypyrimidinyl)disulfide
(30) 2,2xe2x80x2-di(6-chloropyridyl)tetrasulfide
(31) 2,2xe2x80x2-dimororpholinodisulfide
(32) 2,2xe2x80x2-di(8-methoxyquinolyl)disulfide
(33) 4,4xe2x80x2-di(3-methoxycarbonylpyridyl))disusulfide
(34) 2-pyridyl-4-methylthiophenyldisulfide
(35) 2-piperazinyl-4-ethoxymethylphenyldisulfide
(36) 2,2xe2x80x2-di{6-(2-pyridyldithio)pyridyl}disulfide
(37) 2,2xe2x80x2-diquinoxalinyldisulfide
(38) 2,2xe2x80x2-dipteridinyldisulfide
(39) 3,3xe2x80x2-difurazanyldisulfide
(40) 3,3xe2x80x2-diphenanthrolinyldisulfide
(41) 8,8xe2x80x2-diquinolyldisulfide
(42) 1,1xe2x80x2-diphenadinyldisulfide
(43) 4,4xe2x80x2-di(3-carboxylpyridyl)trisulfide
(44) 2,2xe2x80x2-dithiazolinyldisulfide
(45) 2,2xe2x80x2-dipicolyldisulfide
(46) dimethylaminodiethyldisulfide
(47) 2,2xe2x80x2-diperhydroindolyldisulfide
(48) 6,6xe2x80x2-diimidazo[2,1-b]thiazolyldisulfide
(49) 2,2xe2x80x2-di(5-nitrobenzimidazolyl)disulfide
(50) 2,4,6-tris(2-pyridyldithio)-1,3,5-triazine
(51) 2-aminoethyl-2xe2x80x2-hydroxyethyldisulfide
(52) di(2-pyridylthio)methane
(53) 2,4,6-tris(2-pyridyl)-1,3,5-trithiane
(54) 5,5xe2x80x2-diamino-2,11-dithio[3,3]paracyclophane
(55) 2,3-dithia-1,5-diazaindane
(56) 2,4,6-trithia-3a,7a-diazaindene
(57) 1,8-diamino-3,6-dithiaoctane represented by the following formula: 
(58) 1,11-bis(methylamino)-3,6,9-trithiaundecane represented by the following formula: 
(59) 1,14-bis(methylamino)-3,6,9,12-tetrathiatetradecane represented by the following formula: 
(60) 1,10-di(2-pyridyl)-1,4,7,10-tetrathiadecane represented by the following formula: 
The thiocrown ether compound which is useful for the present invention is a cyclic thioether compound. Examples of the cyclic thioether compound include the following compounds (a)-(c).
(a) a thiocrown ether compound having at least one basic nitrogen atom
(b) a thiocrown ether compound having at least one basic nitrogen atom and at least one oxygen atom
(c) a compound in which at least two compounds selected from the group consisting of the above thicrown ether compounds (a) and the thiocrown ether compounds (b) are linked by a C1-C5 alkylene chain.
The above thiocrown ether compound (a) (azathiacrown ether compound) is a compound which can be obtained by replacing an oxygen atom in crown ether with a sulfur atom and has at least one basic nitrogen atom in its molecule. Examples of the thiocrown ether compound include the following compounds.
(i) 1-Aza-4,7,11,14-tetrathiacyclohexadecane represented by the following formula 
(ii) 1,10-Diaza-4,7,13,16-tetrathiacyclooctadecane represented by the following formula 
(iii) 1,10-Diaza-1,10-dimethyl-4,7,13,16-tetrathiacyclooctadecane represented by the following formula 
(iv) 1,16-Diaza-1,16-bis(2-hydroxybenzyl)-4,7,10,13,19,22,25,28-octathiacyclotriacontane represented by the following formula 
(v) 7,8,9,10,18,19,20,21-Octahydro-6H,17H-dibenzo[b,k][1,4,10,13,7,16]tetrathiadiazacyclooctadecane represented by the following formula 
(vi) 3,6,14,17-Tetrathiatricyclo[17.3.1.18,12]tetracosa-1,8,10,12,19,21-hexaene-23,24-diamine represented by the following formula 
(vii) 3,7,15,19-Tetrathia-25,26-diazatricyclo[19.3.1.19,13]hexacosa-1,9,11,13,21,23-hexaene represented by the following formula 
(viii) 6,13-Diamino-1,4,8,11-tetrathiacyclotetradecane represented by the following formula 
The above thiocrown ether compound (b) (azaoxathiacrown ether compound) is a compound which comprises at least one oxygen atom in the above thiocrown ether compound (a). Examples of this compound include the following compounds.
(i) 1-Aza-7-oxa-4,10-dithiacyclododecane represented by the following formula 
(ii) 2,23-Diaza-5,20-dioxa-8,11,14,17-tetrathiabicyclo[22.2.2]octacosa-1,24,27-triene represented by the following formula 
(iii) 1,10-Diaza-4,7-dioxa-13,16,21,24-tetrathiabicyclo[8.8.8]hexacosane represented by the following formula 
The above compound (c) is a compound prepared by linking, for example, two or more of the above azathiacrown ether compounds (a), two or more of the above azaoxathiacrown ether compounds (b), or the above azathiacrown ether compound (a) and the above azaoxathiacrown ether compound (b), through a C1-C5 alkylene chain. Two or more thiocrown ether rings may be linked through the alkylene chain(s). Examples of the above compound (c) include 1,1xe2x80x2-(1,2-ethanediyl)bis-1-aza-4,7,10-trithiacyclododecane represented by the following formula. 
Sulfur-containing Compound in Tin-copper-bismuth Alloy Plating Bath
Unlike the tin-copper alloy plating bath, the tin-copper-bismuth alloy plating bath of the present invention may use 2,2xe2x80x2-dithiodianiline and like dithiodianiline as the sulfide compound containing the basic nitrogen represented by the formula (2). However, other conditions of the sulfur-containing compounds are the same as in the tin-copper alloy plating bath. Specifically, the tin-copper-bismuth alloy plating bath contains, as the sulfur-containing compound, at least one compound selected from the group consisting of the following compounds (i)-(v).
(i) a thiourea compound;
(ii) a mercaptan compound;
(iii) an aliphatic sulfide compound represented by the following formula (1):
Rexe2x80x94Raxe2x80x94[(Xxe2x80x94Rb)Lxe2x80x94(Yxe2x80x94Rc)Mxe2x80x94(Zxe2x80x94Rd)N]xe2x80x94Rfxe2x80x83xe2x80x83(1)
xe2x80x83(wherein the symbols are as described in the above);
(iv) a sulfide compound containing a basic nitron atom represented by the following formula (2):
Rgxe2x80x94[(S)Xxe2x80x94Rh]p-[(S)Yxe2x80x94Ri)]qxe2x80x83xe2x80x83(2)
xe2x80x83(wherein the symbols are as described in the above);
(v) a thiocrown ether compound.
Examples of these sulfur-containing compounds are the same as those of the tin-copper alloy plating bath.
Such tin-copper-bismuth alloy plating bath containing the above-specified sulfur-containing compound has resistance to deposition of copper on the anode by substitution, low dependency of the composition of the plated coating on current density, good bath stability and resistance to turbidness.
Sulfur-containing Compound in Tin-copper-silver Alloy Plating Bath
The sulfur-containing compound useful for the tin-copper-silver alloy plating bath of the present invention are more restricted than those for the tin-copper alloy plating bath and the tin-copper-bismuth alloy plating bath. Specifically, useful are at least one sulfur-containing compound selected from the group consisting of the below compounds (i)-(iv).
(i) an aliphatic sulfide compound (excluding thiodiglycolic acid and thiodiglycol) represented by the general formula (1):
Rexe2x80x94Raxe2x80x94[(Xxe2x80x94Rb)Lxe2x80x94(Yxe2x80x94Rc)Mxe2x80x94(Zxe2x80x94Rd)N]xe2x80x94Rfxe2x80x83xe2x80x83(1)
xe2x80x83(wherein the symbols are as defined in the above);
(ii) a sulfide compound containing a basic nitrogen atom represented by the formula (2):
Rgxe2x80x94[(S)Xxe2x80x94Rh]p-[(S)Yxe2x80x94Ri)]qxe2x80x83xe2x80x83(2)
xe2x80x83(wherein the symbol are as defined in the above);
(iii) a mercaptan compound having at least one basic nitrogen atom; and
(iv) a thiocrown ether compound.
Such tin-copper-silver alloy plating bath which comprises the above-specified sulfur-containing compound has resistance to deposition of copper on the anode by substitution, low dependency of the composition of the plated coating on current density, good bath stability and resistance to turbidness.
Among the sulfur-containing compounds useful for the tin-copper-silver plating bath, as the aliphatic sulfide compounds represented by the formula (1) may be used the same compounds as the aliphatic sulfide compound of the formula (1) useful for the above-mentioned tin-copper alloy plating bath, except that thiodiglycolic acid and thiodiglycol can not be used.
As the sulfide compound containing a basic nitrogen atom of the formula (2) may be used the same compounds as the aliphatic sulfide compound of the formula (2) which is useful for the tin-copper alloy plating bath. Additionally, 2,2xe2x80x2-dithiodianiline and like dithiodianiline may be used.
As the mercaptan compound having at least one basic nitrogen atom may be used acetylcysteine and like aliphatic mercaptan compounds, 5-mercapto-1,3,4-triazole and like aromatic or heterocyclic mercaptan compounds and the like. Incidentally, acetylcysteine has a basic nitrogen atom in an amino group, while 5-mercapto-1,3,4-triazole has a basic nitrogen atom in a triazole ring.
Therefore, the mercaptan compound useful for the tin-copper-silver alloy plating bath of the present invention does not include thioglycol, thioglycolic acid, mercaptosuccinic acid and like mercaptan compounds which do not contain the basic nitrogen atom.
The thiocrown ether compound useful for the tin-copper-silver alloy plating bath of the present invention is the same as the compound which is useful for the above-mentioned tin-copper alloy plating bath.
As mentioned in the above, the sulfur-containing compound useful for the tin-copper-silver alloy plating bath of the present invention are more restricted than those useful for the tin-copper alloy plating bath and tin-copper-bismuth alloy plating bath. When using other compounds than the above-specified sulfur-containing compound, for example, xcex2-thiodiglycol, thioglycol and the like, the dependency of the composition of the alloy plated coating on current density can not be sufficiently lowered.
Amount of Sulfur-containing Compound
In the alloy plating bath containing tin and copper of the present invention, the amount of the sulfur-containing compound in the plating bath is preferably about 0.001-2 mole/l, more preferably about 0.005-0.5 mole/l, in any of the tin-copper alloy plating bath, tin-copper-bismuth alloy plating bath and tin-copper-silver alloy plating bath.
Other Additives
The alloy plating bath containing tin and copper of the present invention may further contain a compound having two or more nitrogen-containing aromatic rings in its molecule, if necessary. The addition of such compound having nitrogen-containing aromatic rings to the plating bath improves the effect of preventing deposition of copper on the anode by substitution.
Examples of the compound having two or more nitrogen-containing aromatic rings in its molecule include 2,2xe2x80x2-bipyridyl, 5,5xe2x80x2-dimethyl-2,2xe2x80x2-bipyridyl, 4,4xe2x80x2-diethyl-2,2xe2x80x2-bipyridyl, 2,2xe2x80x2:6xe2x80x2,2xe2x80x3-terpyridine, 5,5xe2x80x2-diethyl-4,4xe2x80x2-dimethyl-2,2xe2x80x2-bipyridyl, 2,2xe2x80x2-bipyridyl-4,4xe2x80x2-biscarboxylic acid, 1,10-phenanthroline, 5-amino-1,10-phenanthroline, 4,7-dichloro-1,10-phenanthroline, 5-nitro-1,10-phenanthroline, 2-chloro-1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 2-methyl-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, 3,5,6,8-tetramethyl-1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, disodium salt of bathophenanthroline disulfonic acid, 2,4,6-tris(2-pyridyl)-1,3,5-triazine and the like.
The amount of the compound having two or more nitrogen-containing aromatic rings in its molecule to be added to the alloy plating bath containing tin and copper is preferably about 0.002-2 g/l, more preferably about 0.005-0.5 g/l.
The alloy plating bath containing tin and copper of the present invention may further contain an unsaturated aliphatic carboxylic compound, if necessary. The addition of the unsaturated aliphatic carboxylic compound to the plating bath improves the stability of the plating bath and prevents the occurrence of turbidness. It also improves the effect of preventing deposition of copper on the anode by substitution.
Examples of the unsaturated aliphatic carboxylic compound include acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, angelic acid, tiglic acid, maleic acid, fumaric acid, propiolic acid, tetrolic acid, acetylenedicarboxylic acid and like unsaturated carboxylic acids; esters of these unsaturated carboxylic acids such as methyl ester, ethyl ester, propyl ester, butyl ester, hydroxypropyl ester, glycerol ester, polyethylene glycol ester and polypropylene glycol ester; glycerol dimethacrylate, glyceryl diacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate and the like.
The amount of the unsaturated aliphatic carboxylic compound to be added to the alloy plating bath containing tin and copper is preferably about 0.05-100 g/l, more preferably about 0.5-10 g/l.
In addition to the above components, the alloy plating bath containing tin and copper of the present invention may optionally contain conventionally known additives such as surfactants, antioxidants, brighteners, semibrighteners, complexing agents, pH adjusting agents, buffers and the like, depending on its object.
Useful surfactants include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants and the like. The surfactants may be used singly or in combination of two or more kinds. The amount of the surfactants to be added is preferably about 0.01-100 g/l, more preferably about 0.1-50 g/l.
The surfactant is used to improve the appearance, grain fineness, smoothness, adherence, throwing power, etc., of the plated coating. In particular, the surfactant and the above-mentioned sulfur-containing compound act synergistically to effectively lower the dependence of the composition of the plated coating on current density.
The nonionic surfactant for use in the present invention are alkylene oxide adducts which are obtained by addition condensation of 2-300 moles of at least one alkylene oxide selected from the group consisting of ethylene oxide (EO) and propylene oxide (PO) with a compound such as C1-C20 alkanol, phenol, naphthol, bisphenol, C1-C25 alkylphenol, arylalkylphenol, C1-C25 alkylnaphthol, C1-C25 alkoxylated phosphoric acid (its salt), sorbitan ester, styrenated phenol, polyalkylene glycol, C1-C30 aliphatic amine, C1-C22 aliphatic amide and the like.
Thus, the nonionic surfactants may be any of the adducts of EO only, PO only or both EO and PO of the above-mentioned alkanol, phenol, naphthol and like. Specifically, preferable are ethylene oxide adducts of xcex1-naphthol or xcex2-naphthol (i.e., xcex1-naphthol polyethoxylate and the like).
Examples of the C1-C20 alkanol used for the addition condensation of the alkylene oxide include octanol, decanol, lauryl alcohol, tetradecanol, hexadecanol, stearyl alcohol, eicosanol, cetyl alcohol, oleyl alcohol, docosanol and the like.
Examples of the bisphenol used for the addition condensation of the alkylene oxide include bisphenol A, bisphenol B, bisphenol F and the like.
Examples of the C1-C25 alkylphenol used for the addition condensation of the alkylene oxide include mono, di or trialkyl-substituted phenol such as p-butylphenol, p-isooctylphenol, p-nonylphenol, p-hexylphenol, 2,4-dibutylphenol, 2,4,6-tributylphenol, p-dodecylphenol, p-laurylphenol, p-stearylphenol and the like.
Examples of the arylalkylphenol used for the addition condensation of the alkylene oxide include 2-phenylisopropylphenyl and the like.
Examples of the alkyl group of the C1-C25 alkylnaphthol used for the addition condensation of the alkylene oxide include methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, dodecyl, octadecyl and the like. The alkyl group may be at any position of the naphthalene nucleus.
The C1-C25 alkoxylated phosphoric acid (salt) used for the addition condensation of the alkylene oxide is represented by the following formula (a).
Ra.Rb.(MO)Pxe2x95x90Oxe2x80x83xe2x80x83(a)
(in the formula (a), Ra and Rb are the same or different and each represents C1-C25 alkyl, either of which, however, may be H. M represents H or an alkaline metal.)
Examples of the sorbitan ester used for the addition condensation of the alkylene oxide include mono-, di- or tri-esterified 1,4-, 1,5- or 3,6-sorbitan such as sorbitan monolaurate, sorbitan monopalmitate, sorbitan distearate, sorbitan dioleate, sorbitan mixed fatty acid ester and the like.
Examples of the C1-C30 aliphatic amine used for the addition condensation of the alkylene oxide include propylamine, butylamine, hexylamine, octylamine, decylamine, laurylamine, stearylamine, oleylamine, behenylamine, docosenylamine, triacontylamine, dioleylamine, ethylenediamine, propylenediamine and like saturated or unsaturated aliphatic amine and the like.
Examples of the C1-C22 aliphatic amide used for the addition condensation of the alkylene oxide include amides of propionic acid, butyric acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid and the like.
Among the above nonionic surfactants, the alkylene oxide adducts of the C8-C30 aliphatic amine can particularly improve the effects of preventing copper substitution on the anode and stabilize the bath to prevent turbidness by using in combination with the aforementioned specific sulfur-containing compound or by using, in addition to the aforementioned specific sulfur-containing compound, in combination further with a compound having two or more nitrogen-containing aromatic rings in its molecule, unsaturated aliphatic carboxylic compound and the like.
Examples of the cationic surfactant include a quaternary ammonium salt represented by the following formula (b), a pyridinium salt represented by the following formula (c) and the like.
xe2x80x83(R1.R2.R3.R4N)+.Xxe2x88x92xe2x80x83xe2x80x83(b)
(In the formula (b), X represents halogen, hydroxy, C1-C5 alkanesulfonic acid or sulfuric acid; R1, R2 and R3 are the same or different and each represents C1-C20 alkyl; R4 represents C1-C10 alkyl or benzyl.)
R6xe2x80x94(C6H4Nxe2x80x94R5)+.Xxe2x88x92xe2x80x83xe2x80x83(c)
(In the formula (c), X represents halogen, hydroxy, C1-C5 alkane sulfonic acid or sulfuric acid; R5 represents C1-C20 alkyl; R6 represents H or C1-C10 alkyl.)
Examples of the cationic surfactants in the form of salts include lauryltrimethylammonium salt, stearyltrimethylammonium salt, lauryldimethylethylammonium salt, octadecyldimethylethylammonium salt, dimethylbenzyl-laurylammonium salt, cethyldimethylbenzylammonium salt, octadecyldimethylbenzylammonium salt, trimethylbenzyl-ammonium salt, triethylbenzylammonium salt, hexadecyl-pyridinium salt, laurylpyridinium salt, dodecylpyridinium salt, stearylamine acetate, laurylamine acetate, octadecylamine acetate and the like.
Examples of the anionic surfactants include alkylsulfate, polyoxyethylenealkyl ether sulfate, polyoxyethylenealkylphenyl ether sulfate, alkylbenzene-sulfonate, (mono, di, tri)alkylnaphthalenesulfonate and the like. Examples of the alkylsulfates include sodium laurylsufate, sodium oleylsulfate and the like. Examples of the polyoxyethylenealkyl ether sulfates include sodium polyoxyethylene (EO12) nonyl ether sulfate, sodium polyoxyethylene (EO15) dodecyl ether sulfate and the like. Examples of the polyoxyethylenealkylphenyl ether sulfates include polyoxyethylene (EO15) nonylphenyl ether sulfate and the like. Examples of the alkylbenzenesulfonate include sodium dodecylbenzenesulfonate and the like. Examples of the (mono, di, tri)alkylnaphthalenesulfonate include sodium dibutylnaphthalenesulfonate and the like.
Examples of the amphoteric surfactants include carboxybetaine, imidazoline betaine, sulfobetaine, aminocarboxylic acid and the like. Also useful are the sulfated or sulfonated adducts of the condensation products of ethylene oxide and/or propylene oxide with alkylamine or diamine.
Typical examples of the carboxybetaine or imidazoline betaine include lauryldimethylaminoacetatic acid betaine, myristyldimethylaminoacetatic acid betaine, stearyldimethylaminoacetatic acid betaine, cocoamidepropyldimethylaminoacetic acid betaine, 2-undecyl-1-carboxymethyl-1-hydroxyethylimidazolium betaine, 2-octyl-1-carboxymethyl-1-carboxyethylimidazolium betaine and the like. Examples of the sulfated or sulfonated adducts include sulfuric acid adducts of ethoxylated alkylamine, sodium salts of sulfonated lauric acid derivatives and the like.
Examples of the above sulfobetaine include cocoamidepropyldimethylammonium-2-hydroxypropanesulfonic acid, sodium N-cocoylmethyltaurine, sodium N-palmitoylmethyltaurine and the like.
Examples of the aminocarboxylic acid include dioctylaminoethylglycine, N-laurylaminopropionic acid, sodium salt of octyldi(aminoethyl)glycine and the like.
The antioxidants are used to prevent oxidation of tin in the bath. Examples of the antioxidants include ascorbic acid or its salt, hydroquinone, catechol, resorcin, phloroglucinol, cresolsulfonic acid or its salt, phenolsulfonic acid or its salt, naphtholsulfonic acid or its salt and the like.
Useful brighteners include m-chlorobenzaldehyde, p-nitrobenzaldehyde, p-hydroxybenzaldehyde, 1-naphthaldehyde, benzylidenealdehyde, salicylaldehyde, paraldehyde and like aldehyde, vanillin, triazine, imidazole, indole, quinoline, 2-vinylpyridine, aniline and the like.
Examples of the useful semibrighteners include thiourea compounds, N-(3-hydroxybutylidene)-p-sulfanilic acid, N-butylidenesulfanilic acid, N-cinnamoylidene-sulfanilic acid, 2,4-diamino-6-(2xe2x80x2-methylimidazolyl (1xe2x80x2))ethyl-1,3,5-triazine, 2,4-diamino-6-(2xe2x80x2-ethyl-4-methylimidazolyl(1xe2x80x2))ethyl-1,3,5-triazine, 2,4-diamino-6-(2xe2x80x2-undecylimidazolyl(1xe2x80x2))ethyl-1,3,5-triazine, phenyl salicylate, benzothiazole compounds and the like. Examples of the benzothiazole compounds include benzothiazole, 2-methylbenzothiazole, 2-(methyl-mercapto)benzothiazole, 2-aminobenzothiazole, 2-amino-6-methoxybenzothiazole, 2-methyl-5-chlorobenzothiazole, 2-hydroxybenzothiazole, 2-amino-6-methylbenzothiazole, 2-chlorobenzothiazole, 2,5-dimethylbenzothiazole, 2-mercaptobenzothiazole, 6-nitro-2-mercaptobenzothiazole, 5-hydroxy-2-methylbenzothiazole, 2-benzothiazolethioacetic acid and the like.
The complexing agents are used mainly for stabilizing and promoting the dissolution of copper in the bath. Examples of the useful complexing agents include gluconic acid, glucoheptonic acid, ethylenediamine, ethylenediaminetetraacetic acid (EDTA), diethylene-triaminepentaacetic acid (DTPA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), iminodipropionic acid (IDP), hydroxyethylethylenediaminetriacetic acid (HEDTA), triethylenetetraminehexaacetic acid (TTHA), oxalic acid, citric acid, tartaric acid, Rochelle salt, lactic acid, malic acid, malonic acid, acetic acid, salts of these compounds, thiourea or its derivatives and the like.
Useful pH adjusting agents include hydrochloric acid, sulfuric acid and like acids, ammonium hydroxide, sodium hydroxide and like bases.
Useful buffers include boric acids, phosphoric acids, ammonium chloride and the like.
The concentration of the above additives in the alloy plating bath containing tin and copper of the present invention may be suitably selected depending on the method by which the plating bath is used, such as the barrel plating, rack plating, high-speed continuous plating, rackless plating and the like.
Plating Conditions
When electroplating is conducted with the alloy plating bath containing tin and copper of the present invention, the bath temperature is preferably about 0xc2x0 C. or higher, more preferably about 10-50xc2x0 C. The cathode current density is preferably about 0.01-150 A/dm2, more preferably about 0.1-30 A/dm2.
The pH of the bath may be in the broad range of acidic to approximately neutral, particularly preferably in the range of weakly acidic to strongly acidic.
The alloy plating bath containing tin and copper of the present invention is a lead-free plating bath. The plated coating formed from the plating bath of the invention has as high soldering strength as conventional tin-lead alloy coatings. Therefore, the alloy plating bath containing tin and copper of the invention is highly useful as a safe plating bath which is capable of forming a plated coating excellent in soldability especially when the article to be plated is an electrical part or electronic part. The electrical part or electronic part to be plated is not restricted, and may be, for example, semiconductor devices, connectors, switches, resistors, variable resistors, condensers, filters, inductors, thermistors, quartz resonators, lead wires, printed boards or the like. The thickness of the plated coating is not critical and usually about 1-20 xcexcm.
The alloy plating bath containing tin and copper of the present invention produces the prominent effects described below.
(1) The alloy plating bath containing tin and copper of the invention can prevent the deposition of copper on the tin anode by substitution during electroplating. This is presumably because the sulfur-containing compound in the plating bath affects the copper salt in the bath and lowers the standard electrode potential of the copper, inhibiting the deposition of the copper on the tin anode by substitution.
In general, the copper salt concentration in the alloy plating bath containing tin and copper is adjusted to be lower than that of tin(II) salt. In the alloy plating bath containing tin and copper of the invention, however, the copper salt concentration in the bath can be appropriately maintained since the copper is hardly deposited on the tin anode. For this reason, unlike in conventional plating baths in which the proportion of the copper in the plated coating may be disadvantageously lowered due to the copper substitution on the anode, the alloy plating bath containing tin and copper of the invention improve the constancy of the Sn/Cu ratio in the plated coating without the supply of copper salt.
(2) The alloy plating bath containing tin and copper of the invention can form a plated coating having a constant composition at a current density widely ranging from low current density to high current density, providing an alloy plated coating containing tin and copper having low dependency of the plated coating composition on current density.
For instance, the alloy plating bath containing tin and copper of the invention can easily provide a highly practical tin-copper eutectic alloy containing 1.3 mole % of Cu.
(3) The alloy plating bath containing tin and copper of the present invention has a good stability with time and thus hardly becomes turbid even after about 1 month from the preparation of the bath.
The turbidness of the alloy plating bath containing tin and copper results from the oxidation of divalent tin into tetravalent, which presumably occurs in the following cycle. In the alloy plating bath containing tin and copper, Cu2+ reacts with the tin salt to oxidize Sn2+ to Sn4+. The copper ions (Cu+) reduced by the tin salt is oxidized to be Cu2+ again by the reduction of oxygen which takes place at the same time with the oxidation of the tin. The resulting Cu2+ again disadvantageously reacts with the Sn2+ in the bath.
According to the alloy plating bath containing tin and copper of the present invention, the sulfur-containing compound in the bath stabilizes the copper salt. Hence, assumably, the copper ions do not react with Sn2+ in the bath, whereby the oxidation of tin is inhibited and the turbidness of the bath is prevented.
(4) The tin-copper-silver alloy plating bath of the present invention comprises silver which is difficult to be stably dissolved in the bath. However, the bath does not decompose for a long period after the preparation of the bath, and can provide a plated coating having constant composition. This is presumably because the specific sulfur-containing compound used as an additive stabilizes the silver in the bath.
(5) When the alloy plating bath containing tin and copper of the present invention further comprises a compound having two or more nitrogen-containing aromatic rings in its molecule, the deposition of copper on the tin anode by substitution during electroplating can be prevented more effectively.
(6) When the alloy plating bath containing tin and copper of the present invention further comprises an unsaturated aliphatic carboxylic compound, the deposition of copper on the tin anode by substitution during electroplating can be prevented more effectively. In addition, the stability of the plating bath is improved and the bath is prevented from becoming turbid over a long period of time.
(7) When the alloy plating bath containing tin and copper of the present invention further comprises a surfactant, the formed plated coating is given greatly improved appearance, grain fineness, smoothness, adherence, throwing power and the like. Therefore, the commercial value of the plated product can be increased.
Particularly, the surfactant and the sulfur-containing compound, when used in combination, act synergistically to further lower the dependence of the composition of the alloy plated coating on current density.
(8) The plated coating formed from the alloy plating bath containing tin and copper of the present invention is a lead-free solder plated coating. Thus, the plated coating has little adverse effects on the human body and the environment. Additionally, the plated coating is a highly practical lead-free solder plating because of its high soldering strength and melting point similar to that of tin-lead alloy plating.
Furthermore, the tin-copper alloy plating is unlikely to form cracks and the tin-copper-bismuth alloy plating can effectively prevent the formation of both whiskers and cracks. Thus, these baths are prospective substitutes for the tin-lead alloy plating.